The present invention generally relates to a hydraulic unit and more particularly relates to a hydraulic control unit used for vehicle brake control.
DE 44 38 163 A1 discloses a hydraulic unit used in vehicle brake applications. Special provisions are necessary for arranging this hydraulic unit in an automotive vehicle in order to comply with specifications with respect to the operability of the system, e.g. a salt spray test, and hence to satisfy the later everyday demands placed on the resistance to salt water and splash water during operation.
A joint ventilation system ensures that the ventilation and venting of the hollow chambers in the hydraulic unit for the purpose of pressure compensation relative to the atmosphere takes place exclusively by way of one single point of ventilation which is in connection to a pressure compensation channel of the ventilation system. This point of ventilation includes a wall portion which is permeable to gas, but impermeable to fluid and solid particles.
Alternatively, the point of ventilation may be provided with a non-return valve which protects the hollow chambers against the ingress of moisture.
The fluid-impermeable wall portion prevents, however, the discharge of leakage fluid of the pump which initially collects in the crank chamber of the pump and can dam up towards the electric motor and, hence, in the present embodiment, also in the direction of the other function elements of the hydraulic unit which are connected by way of the ventilation system so that already small quantities of leakage fluid in the electric motor may cause malfunctions of the hydraulic unit.
In view of the above, an object of the present invention is to improve upon a hydraulic unit of the type referred to hereinabove so that leakage fluid of the pump can be discharged reliably out of the crank chamber into the open air without inhibiting the exchange of air and, thus, ventilation of the hydraulic unit.